For proper utilization of natural or man-made fibers it is essential to have precise, accurate, and basic tensile characteristics of the fibers. To illustrate, in the making of yarn from cotton or polyester staple, in the researching of genetic influences upon characteristics of cotton or wool, or in the production of man-made fibers from carbon or glass, data relating to the tensile characteristics of the fibers commonly need to be compiled, studied, and utilized. In most basic terms, individual fibers are the building blocks, the basic materials of construction, the essence of textile yarns. It follows that their tensile characteristics are a major determinant in their proper utilization or in their preparation. Such tensile characteristics are not readily available with prior art instruments and the broadest objective of this invention is convenient and rapid provision of accurate and precise tensile data for fibers.
As used herein, the term "tensile" will be understood to include tension-elongation characteristics and cross-sectional characteristics. For example, the traditional material characteristic of tensile stress is simply the ratio of breaking force divided by cross-sectional area; common dimensions for tensile stress are pounds/inch.sup.2 or newtons/m.sup.2. As a second example, percentage elongation is sometimes taken as the elongation for which Hooke's Law holds (when incremental force is directly proportional to incremental elongation) divided by the untensioned length (gauge) of the material times 100%. Note that this definition of elongation is not general; it excludes elongation components when the force is small, i.e., "crimp" or "slack", or when force is not linear with elongation, i.e. plastic deformation.
It is especially desirable that such tensile data be generated conveniently and quickly and in sufficient quantities to permit the statistical analysis of the fibers' properties.
Known instruments used for obtaining tensile data from a bundle of fibers are not capable of providing data on individual fibers. In the textile industry, it is traditional to test bundles of staple fibers as opposed to single fibers. In part, the rationale behind this procedure is that fibers are normally used in bundles such as in cotton yarn (thread). However, these traditional test procedures cannot provide information about the properties of single fibers which comprise the bundle because of the impossibly complex interactions of their nonlinearities or of their distributions in peak breaking tension, elongation at break, crimp, or fiber-to-fiber friction. Even if the bundle extension rate were made extremely low and the transducer made very sensitive, so that individual fiber breaks could be observed, the exact shape of the tension-elongation diagrams of individual fibers cannot possibly be determined in general. This impossibility applies if the number of fibers in the bundle is two or more! And practical transducer responses even further preclude direct measurement of true single fiber properties from bundle tests. Even if the sensitivity of the force transducer is made very high, the data obtained from a fiber bundle test is masked by damped oscillatory response or ringing of the force transducer. That is, as individual fibers in a bundle break, a ringing oscillation is inherently set up in the test device that may distort data. Since the fibers of a bundle break at varying elongations, this ringing effect is randomly occurring throughout the majority of the test. Ringing may not significantly affect the data as to the entire bundle but it frustrates any attempt to derive precise data as to individual fiber characteristics.
Existing instruments for testing a single fiber, such as the Instron force-elongation tester, are very slow to use due to tedious manual procedures involved in preparing the fiber for testing. In that part of the textile industry using staple fibers, individual fiber testing is seldom done because the statistical quality of data thus obtained is not currently viewed as useful as bundle test data and because such single fiber tests are more expensive to acquire. For monofilament fibers, such single fiber testing is used, in spite of its expense or poor statistical basis.
Bundle tests and yarn tests, although well-established and widely used, defy rational explanation in engineering terms unless true single fiber tensile properties are known and properly and widely utilized. Yarn is, of course, a special bundle constructed of many single fibers. Absence of rational explanations of yarn properties, in terms of basic fiber tensile properties, is thus inhibiting advances in the fiber-to-yarn engineering process.
It is therefore, again, an objective of this invention to provide apparatus and methods for testing at least single fiber tensile properties, wherein such data are obtained conveniently, rapidly, accurately, and precisely and in sufficient quantities to be statistically meaningful. It is a further object of this invention to provide means for simulating practical bundles, including test bundles and yarn, the most practical bundle.